trans 1,2-dichloroethylene

The Last Chlorinated solvent?

The era of chlorinated solvents began in the early 20th century. Initially used to replace petroleum based solvents, Carbon tetrachloride and Trichloroethylene were extensively used as dry cleaning solvents until being replaced by Perchloroethylene(Tetrachloroethylene) in the 1950s. Following some questionable toxicity studies on dry cleaning solvents, chemicals such as 1,1,1 Trichloroethane, CFC 113, HCFC 141b, and Methylene chloride gained acceptance in the dry cleaning, electronics industry, polymer manufacturing, vapor degreasing, and foam blowing, while Carbon tetrachloride, Perchloroethylene, and Trichloroethylene saw a decline in their use. Over the next three decades concerns over environmental impact and toxicity have all but eliminated most of these chemicals. If we look at a short list the following chemicals have been eliminated or severely restricted.

Restricted or eliminated due to Toxicity:

Restricted or eliminated due to Environmental Concerns:

  • Carbon Tetrachloride
  • Perchloroethylene
  • Trichloroethylene
  • Methylene chloride
  • N-Propyl bromide
  • 1,1,1 Trichloroethane
  • CFC 11
  • CFC 113
  • HCFC 141b
  • HCFC 225


It should also be noted that following the Montreal Protocol, many environmental groups, regulators, and politicians actively demanded the elimination of halogenated solvents even though the toxicity data and environmental data did not support these conclusions. Regardless of the science, we have seen many useful chemicals eliminated.

The exception to this rule has been Trans. The Trans molecule is chemically positioned to not be involved in ozone depletion, is not a global warmer, and has a low MIR value. So while Trans is a VOC, its MIR value does allow it to be used in reactivity based formulas successfully. In addition, it can be blended to achieve mass based compliant formulas and it can be tailored to meet various applications requirements. Trans has a typical odor for a chlorinated solvent which most people do not find objectionable.

If we evaluate Trans as to its characteristics it would be described as follows:

  • Solvency: strong solvent, KB value > 100
  • Evaporation: Fast
  • Density: high > 1.00
  • Odor: Light
  • Solubility: compatible with petroleum solvents and propellants, alcohols, ketones, glycol ethers, fluorinated solvents and propellants, but not recommended for water based formulas

When we review the positive aspects of this solvent, one asks why it has not been more widely used. The simple answer is price. Although Trans has been widely used in electronic and specialty cleaning products, the transition into more general cleaning products has not widely occurred.

For many years methylene chloride, perchloroethylene, and trichloroethylene have been available at pricing similar to hydrocarbon solvents. Trans on the other hand was priced significantly higher with no additional benefit to justify this price. Through the efforts of DCPC, Trans is now more competitively priced and it alone does not have the environmental and toxicity problems shared by other chlorinated solvents.

In recent years formulators have seen increasing movement towards water based solvents. For many applications this move is the correct choice. However, Trans can be a valuable tool for many product type:

  • Cleaner/Degreasers
  • Spot Lifters
  • Dry Cleaners
  • Paint Strippers
  • Specialty Cleaners/Electronics
  • Cosolvents in paints, adhesives, lubricants, penetrating fluids

To qualify these uses, one can look at the characteristics of Trans. As a strong solvent, it is capable of dissolving and removing many types of materials. As a fast evaporator, it can be used to accelerate the drying of cosolvents and resins in many formulations. The high density of Trans, allows it to penetrate into cracks and crevices even in the presence of moisture. In addition, it can be formulated with alcohols or glycol ethers to solubilize the water and to speed up evaporation. When used in penetrate/ lubricant formulas it provides excellent "creep" and penetration and after solvent evaporation it leaves the protective lubricant film with no undesirable residue.

Since Trans is compatible with most solvent groups, it is easy to blend it with various chemicals to meet VOC regulations, pricing needs, and provide solvency and evaporation rates as required by the formulation.

Let's look at a sample formula to illustrate how we can build on the Trans concept:

Trans Sample Formulation - Paint Stripper

Chemical

Function

WT%

Trans

Strong Solvent

30%

Petroleum Solvent

High Flash(VOC exempt)

20%

Acetone

Exempt Solvent

10%

Butyl Carbitol

Cosolvent

26%

A-108

Propellant

14%


This formula has a VOC content of 44%. The VOC level could be varied to meet new category requirements or change in VOC regulations. One could add surfactants to make a water rinse able formulation and the levels of the cosolvents could be changed to increase or decrease evaporation. One could add a gelling agent to provide for a thick/ clinging formula. The cost could be reduced by the selection of solvents and changing the ratios of solvents.

1,2 Transdichloroethylene is not a new chemical, but it does have new life as we see the further regulation of Methylene chloride, Perchloroethylene, Trichloroethylene, and NPB. In a world of decreasing choices for the formulators, the availability of Trans is a positive advantage.

 

Aerosol Propellants

Blowing Agents

Alternative Fuels

Physical Properties

Technical (MSDS)

General Literature

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